This invention relates to a method and apparatus for vacuum bag molding of composite materials.
A common method of manufacturing articles from composite materials involves laying up a number of sheets of uncured resin-impregnated filaments called "prepregs" on a suitable forming tool, subjecting the prepregs to heat and pressure in order to coalesce the sheets, molding the prepregs to the configuration of the conforming tool, and subsequently gelling the resin. Finally, the resin is cured by further heat treatment to fix the resultant configuration of the molded article.
Vacuum bag molding is often employed to carry out this method wherein the laid-up prepregs are placed on the forming tool and then enclosed by an impermeable membrane commonly referred to as a "vacuum bag." The volume enclosed by the vacuum bag is evacuated and the assembly is heated up on a rising temperature schedule, and the prepregs coalesce to form the molded article. The rising temperature schedule ensures that the uncured resin is sufficiently mobile to permit maximum consolidation.
In typical vacuum bag molding, the vacuum bag assembly includes a forming tool, prepreg sheets, a porous release sheet, a breather material, and the vacuum bag. The conventional vacuum bag approach requires pores in the release sheet--it is widely believed by those skilled in the art that a porous release sheet is essential to allow gases and vapors (i.e.,volatiles) to escape through a path normal to the prepregs.
While the conventional vacuum molding method can provide an effective method of manufacturing articles from composite materials, it would be desirable to employ a nonporous release sheet for the vacuum bag molding process. Using a nonporous release sheet would provide an inexpensive alternative to the porous release sheet and therefore reduce composite part production cost.